Industrial Maintenance & Reliability · SOP
HVAC Heat Exchanger Tube Brushing and Eddy Current Test Prep
This standard operating procedure outlines the complete work sequence for mechanically cleaning heat exchanger tubes and preparing the exchanger for non-destructive eddy current testing. Following this procedure ensures accurate defect detection, maximum heat transfer efficiency, and compliance with industry maintenance standards.
Estimated Time
120 min (per bundle)
Difficulty
Advanced
Regulation
CSA B52 / ASME PCC-1
Version
1.0
Purpose
The purpose of this standard operating procedure is to provide a uniform, repeatable methodology for cleaning heat exchanger tubes using mechanical brushing, followed by preparatory steps for eddy current testing. Proper execution restores thermal performance, removes fouling and corrosion debris, and ensures that eddy current signals are not obscured by residual deposits — enabling reliable condition assessment of every tube in the bundle.
Scope
This procedure applies to all shell-and-tube heat exchangers within HVAC and industrial process systems at [FACILITY NAME] that require periodic tube cleaning and non-destructive evaluation. It covers straight-tube bundles with standard ferrous and non-ferrous metallurgies (carbon steel, stainless steel, copper, admiralty brass). Excluded are U-tube bundles, finned tubes, and microchannel exchangers which demand alternate cleaning protocols referenced in Appendix C.
Safety Precautions
- Complete zero‑energy state verification: lockout all electrical, steam, and chilled water supply valves. Tag out the exchanger and associated pumps with a personal danger tag. Verify isolation with a pressure gauge bleed.
- Wear safety glasses with side shields, cut‑resistant gloves (ANSI A4), hearing protection (if brushing tools generate >85 dBA), and a respirator (N‑95 minimum) when heavy scale or biological growth is present. Full‑face shield required during compressed‑air debris blow‑out.
- Allow the heat exchanger to cool to <40 °C before opening. Surface temperature must be verified with a non‑contact IR thermometer. Never break a flange on a pressurized or hot vessel.
- Work area containment: erect a drip‑curtain around the tube bundle to capture loose debris and chemical residue. Use a HEPA‑rated vacuum for continuous airborne particulate control.
Required Tools & Materials
- Tube brush set (nylon or stainless steel bristle) with diameter 0.005" – 0.010" over tube ID
- Flexible extension rods (3/8″ hex drive, 36″ segments) with quick‑connect couplers
- Power drill (variable speed, 0–1200 rpm minimum)
- HEPA‑rated industrial vacuum with crevice and brush attachments
- Compressed air blow gun with regulator set to 90 psi max
- Eddy current testing instrument (e.g., Zetec MIZ‑21C or Olympus NORTEC 600) with appropriate probe (absolute or differential, 200–400 kHz)
- Calibration reference standard (ASTM E309 / E215 with notched and through‑wall hole defects)
- Tube sheet inspection camera (borescope with 5.5 mm diameter, 2‑way articulation)
- Personal protective equipment per Section 3
- Lockout/tagout kit: padlocks, hasps, danger tags, bleeder valves
- Containment drip‑curtain and absorbent pads
Procedure: Step-by-Step
1
Isolate & Lockout — Confirm zero‑energy state using the facility LOTO procedure. Attach lock and tag to the exchanger isolation valves and circuit breakers. Bleed any residual pressure from both shell and tube sides. Allow surfaces to cool below 40 °C before proceeding.
2
Access & Document — Remove all tube access covers and channel head bolts using an impact wrench with a torque stick. Place gaskets in labelled bags. Photograph the tube sheet before brushing — note any heavy fouling, corrosion, or blocked tubes. Assign a tube number grid (rows A–Z, columns 1–n) matching the eddy current data sheet.
3
Brush Selection & Attachment — Select a brush 0.005″–0.010″ larger than actual tube ID measured with an internal tube gauge. Attach brush to the extension rod using the nut‑and‑cone locking system. Test run the brush in a clean tube stub to confirm full circumferntial contact without binding.
4
Mechanical Brushing — Insert brush at low speed (~200 rpm). Advance slowly with steady forward pressure — do not exceed 15 seconds per pass. Retract at slow speed while rotating. Repeat 3–5 passes per tube until brush emerges with minimal debris. Rotate the brush one‑quarter turn between passes to maximize coverage.
5
Debris Removal — Attach the HEPA vacuum crevice tool to each tube opening immediately after brushing. Run the vacuum for 10 seconds per tube. Precaution: Use compressed air blow‑gun only on tubes that are fully dry and only if water hammer risk is absent — aim away from yourself and others. Never combine air blow‑gun with an open vacuum nearby (cross‑contamination risk).
6
Visual Inspection — Use the borescope to inspect a 10 % sample of tubes (every 10th tube per row). Note: pitting, gouges, rolled‑out marks, or through‑wall perforations. Mark any tube that shows >20 % wall loss with a yellow tag — skip eddy current testing and flag for immediate plugging per ASME PCC‑1.
7
Eddy Current Calibration — Set up the eddy current instrument with the correct probe frequency (typically 200 kHz for carbon steel, 400 kHz for admiralty brass). Run the probe through the calibration standard twice and verify that the signal‑to‑noise ratio exceeds 3:1 for the reference notch. Record calibration drift — reject if >5 %.
8
Eddy Current Data Acquisition — Insert the probe into each tube from the tube sheet face. Maintain a steady pull speed of 0.5 m/s ± 0.1 m/s. Capture impedance‑plane traces for every tube. On encountering anomalies, stop, mark the tube with a red tag, and record the signal type (volumetric, pitting, dent). Proceed tube‑by‑tube until the bundle is complete.
9
Documentation & Restoration — Transfer all eddy current data to the tube‑inspection report spreadsheet. Highlight tubes that fail acceptance criteria (≥40 % wall loss for non‑ferrous, ≥30 % for ferrous). Replace channel head gaskets, reinstall covers, and torque bolts in a cross‑pattern sequence to manufacturer spec. Remove LOTO devices and return the exchanger to service. Submit report to the maintenance supervisor within 24 hours.